Removal of carbonaceous deposits from process equipment



deposits,

Patented June 23, 1953 REMOVAL OF CARBONACEOUS DEPOSITS FROM PROCESS EQUIPMENT Christopher A. Murray, Nederland, Tex., assignor to Pure Oil Company, Chicago, 111., a corporation of Ohio No Drawing. Application December 27, 1949, Serial No. 135,295

4 Claims.

The present invention relates to a method of removing carbonaceous deposits from refinery and chemical manufacturing equipment and relates more particularly to the use of spent alkylation sulfuric acid to remove carbonaceous coke inorganic and organic scales and various corrosion and side reaction by-products from the surfaces of processing equipment.

In the process of treating hydrocarbon oils, conducting various chemical reactions, treating organic material under conditions producing carbonaceous deposits, the various pieces of plant equipment become caked or coated with the byproducts and residues of the reaction necessitating tedious clean-out methods. Generally, after the bulk of the cake has been scraped or chipped out, 98 percent hot fuming sulfuric acid is employed at temperatures from 212 F. to 300 F. to remove the more tenacious and inaccessible deposits. In extreme instances it often becomes necessary to dismantle the equipment and remove the last traces of the deposits by mechanical means even after this 98 percent acid treatment.

.It is an object of this invention to provide a method of removing carbonaceous and by-product residues and coke deposits from process equipment.

It is another object of this invention to provide a method of removing inorganic deposits which contain some carbonaceous process equipment.

It is a third object of this invention to decrease the cost and increase the efficiency of methods of reconditioning process equipment.

It is a fourth object of this invention to facilitate the removal of carbonaceous deposits from refinery processing equipment by treatment with heated spent alkylation sulfuric acid.

It is a fifth object of this invention to utilize a Waste product from the sulfuric acid alkylation process.

Other objects and embodiments of this invention will become apparent as the description thereof progresses.

In the alkylation of isoparaffinic hydrocarbons, such as isobutane, with olefins, such as butenes, to produce the many higher molecular weight branched chain paraffinic hydrocarbons, called the alkylate, widely used in aviation motor fuel, there results a spent alkylation acid or acid sludge. Such a process is disclosed in United States Patents Numbers 2,341,487, 2,420,369,. and 2,428,506. Before this spent acid can be reused for catalytic purposes, ,itmust. be recovered and materials from fortified. Such procedure is expensive, and as a result, much of the spent acid or acid sludge is generally discarded. This discarded acid containing from to of sulfuric acid, being unsuitable for further use as a catalyst in the alkylation process, is at present an economic loss and presents a disposal problem.

My invention involves a method for cleaning adherent carbonaceous deposits from metal processing equipment by the application of spent alkylation sulfuric acid, containing about 85 percent sulfuric acid and small amounts of hydrocarbon sulfates and other products of the alkylation reaction, at a temperature of F. or lower and finally draining the acid from the equipment and flushing the equipment with an aqueous solvent. This spent alkylation acid can also be used to disintegrate organic binding materials which hold inorganic scales and corrosion products or by-product sludges which adhere to the inside of processing equipment.

The main difficulty with the hot fuming 98 percent acid treatment is that the resultant efiluent forms jells and solid cakes which cannot be removed by subsequent water flushing. If hot fuming sulfuric acid of greater strength than 98 percent is used, the resultant efiluent is transformed into a sticky amorphous rubbery residue which is very difficult to remove from the equipment by flushing or mechanical means. I have discovered that if spent alkylation acid is used at 156 F. or lower temperature for these cleaning operations, the resultant slurry or efiiuent is not sticky, has no tendency to solidify or gel, and is easily pumped from the system leaving the surfaces therein clean and without deleterious cake or scale.

I believe that the spent alkylation acid works as it does because the hydrocarbon sulfate complexes, olefin polymers, sulfonic acids and hydro carbons present in the spent acid, aid in the rapid penetration of the carbonaceous residue or cake and also prevent the formation of acid-cake, acid-jell, or acid residues which are not easily flushed out with water. The amount of organic material present in the spent alkylation acid in the form of hydrocarbon sulfates or otherwise, may vary from 2 to as much as 10% or more. Water may be present in the spent acid in amounts varying between 2 to 15% without detracting from the ability of the spent alkylation acid to remove deposits.

In the actual operation of the present invention it is merely necessary to treat the carbonaceous deposit within the equipment with sufliclent spent alkylation acid at relatively low temperatures, drain the acid from the equipment and flush with an aqueous solvent. Temperatures as low as 150 F. give good results and the reaction is more easily controlled than when using 98 percent fuming sulfuric acid at higher temperatures. This is a distinct advantage since handling hot acid solutions is beset with serious occupational hazards. In addition, there is the added expense of maintaining the 98 percent hot fuming acid at the higher temperatures.

The invention is applicable to the removal of carbonaceous coke deposits resulting from numerous reactions conducted on an industrial basis. By way of illustration only, the process of the present invention will be described in connection with the cleaning and reconditioning of reboilers of an alkylation unit. However, the invention should not be limited thereby, since it is applicable wherever there is the problem of removing tenacious deposits caused by reactions generally of an organic nature, wherein carbonaceous sludges and coke residues build up in processing equipment due to extreme conditions of temperature and pressure. The lines, reboilers, furnace tubes, reactors and all vessels in refinery and chemical process operations can, therefore, be cleaned and freed of carbonaceous deposits in accordance with this invention.

During the alkylation of isoparaffins with olefins in the presence of a catalyst, the hot gas oil belt reboilers, the gas oil lines, and gas oil surge drum become caked with a tenaciously adhering carbonaceous deposit. If, for example, the reboilers are removed, dismantled and manually cleaned and replaced, they are still too dirty to be placed in operation. If in accordance with this invention, alkylation spent acid is charged to the reassembled reboilers at a temperature of at least about 150 F. for about 30 minutes, and l continuously circulated therethrough, the result ant effluent is easily pumped from the unit. After flushing the remaining acid from the reboilers, with the addition of an inhibitor in the flush water, the unit is found to be thoroughly clean and free from carbonaceous deposits. The acid treatment is advantageously followed by an alkali wash and draining with subsequent water flush to complete the treatment.

Technical Bulletin T-3 of October 1948, published by The International Nickel Company, Incorporated, shows on' page 30, Table 44, that various metal alloys are quite resistant to attack by 85% sulfuric acid containing hydrocarbons. Table 2, page 7 of this bulletin shows that the rate of corrosion of alloys in boiling sulfuric acid solutions of 10%, 19%, 75% and 96% concentration is highest in the 75% acid with the 98% acid holding second place in its ability to corrode most of the alloys tested. Cast iron and mild steel generally show corrosion rates above that of alloys, especially in acids of concentrations around to and for this reason when cleaning equipment constructed of these materials, it is expedient to incorporate a corrosion inhibitor or passivator in the acid cleaning solutions or subsequent water flushing steps used in accordance with this invention. The organic type inhibitors universally used in acid pickling baths or to inhibit the corrosion of metal parts in an oil well during acidization may be applied in practicing the present process. Some of these organic inhibitors are butyl sulfide, thioureas, alkyl mercaptans, cresols, organic amines, crotonaldehyde, formaldehyde, and compounds like ethyl selenide and the various toluidines and xylidines. Also inorganic inhibitors such as chromates and arsenates and copper sulfate are effective.

Thus, there has been described a method of cleaning and servicing chemical process equipment in a manner which is expedient and theroughly efficient and economical. It may also be found that after treating and cleaning the surfaces of equipment in the manner of the present invention, any subsequently adhering carbonaceous deposits are more easily removed by mechanical means prior to subsequent spent acid treatment and thereby there is experienced a dual improvement with resultant saving in labor costs and shortened down-time.

The amounts of spent alkylation acid will depend on the quantity of carbonaceous deposits to be removed. In general, one gallon of spent alkylation acid containing sulfuric acid will decompose 15 pounds of carbonaceous coke found in the hot gas oil belt reboilers of an alkylation unit. The amount of spent acid used can be adjusted according to the particular conditions or type of deposit to be removed and a smaller amount of total acid may accomplish a given cleaning operation. A treating time of one-half hour is generally sufficient although longer or shorter times may be employed as the exigencies of the particular situation dictate.

One particular advantage of the present process is that aggregates of inorganic deposits, such as aggregates of deposits of various metal sulfides, oxides, metal salts or organic metal compounds, containing a small amount of organic material which is attacked by the spent alkylation sulfuric acid, can be readily disintegrated and the inorganic deposits put in a form easily removed from the process equipment. In conducting such a cleaning operation, smaller amounts of spent alkylation acid may be employed since the acid is only reactable with the organic carbonaceous portion of the deposit. The water flush or alkaline wash are not entirely necessary but serve to complete the cleaning process in conformance with accepted standards.

Whether or not a particular piece of equipment will need to be dismantled and scraped prior to treatment in accordance with this invention will depend on the extent and quantity of deposit therein. For some pieces of equipment wherein conditions are optimum for the formation of these deleterious deposits, and pre vious experience has taught that frequent cleaning is necessary, it may be expedient to apply the spent alkylation sulfuric acid treatment in accordance with this invention in more frequent intervals, without dismantling the equipment. This is possible since the necessary piping arrangements can be installed in the equipment to convey the spent alkylation acid therethrough followed by alkali and water flushing and dismantling can be avoided entirely. The labor required to shut off the equipment or by-pass it and pass spent alkylation acid therethrough will be much less than is required for dismantling and scraping after the deposits have been allowed to build up too high.

In some processes Where intermittent application of spent alkylation acid will not conflict with the process or contaminate the product, such intermittent injection of spent alkylation sulfuric acid may be used to purge or prime the system at regular intervals and prevent the formation of carbonaceous deposits entirely. Spent acids containing as much as of hydrocarbon sulfates may require less time.

After cleaning process equipment, the effluent spent acid will ordinarily be subject to disposal since, unless the acid content is not below about 85%, it is not expedient or economical to attempt revivification of the effluent acid. However, in certain instances a saving can be experienced in that by allowing the efliuent spent acid to settle and the organic and inorganic sludge drained off, the acid can be reused. After two or three applications of the same spent acid solution to the cleaning procedure, it is generally ready for disposal by the usual methods.

What is claimed is:

1. A method of removing carbonaceous deposits from the surfaces of chemical process equipment comprising applying thereto spent alkylation sulfuric acid, draining the acid from the equipment after about 30 minutes and flushing the equipment with an aqueous solvent.

2. A method of removing carbonaceous deposits from the surfaces of chemical process equipment comprising contacting said deposits with spent alkylation sulfuric acid at a temperature of at least about 150 F., and flushing the equipment to remove said deposits.

3. A method of cleaning chemical process equipment of carbonaceous deposits comprising subjecting said deposits to contact with sumcient spent alkylation sulfuric acid containing at least sulfuric acid and minor portions of byproducts from an alkylation reaction to loosen said deposits, said contact taking place at a temperature of at least about F., draining the acid from the equipment and thereafter flushing the equipment with an aqueous solvent. 4. A method of removing inorganic deposits mixed with carbonaceous material from chemical process equipment comprising contacting the deposits with spent alkylation sulfuric acid containing at least about 85% sulfuric acid and minor portions of by-products from the alkylation reaction, at a temperature of at least about 150 F. to disintegrate said deposits, flushing the equipment with water, treating the equipment with sufiicient aqueous alkali solution to neutralize the efliuent from the acid treatment, and then again flushing the equipment with water.

CHRISTOPHER A. MURRAY.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,419,076 Horsley Apr. 15, 1947 FOREIGN PATENTS Number Country Date 510,733 Great Britain Aug. 8, 1939 

1. AN METHOD OF REMOVING CARBONACEOUS DEPOSITS FROM THE SURFACES OF CHEMICAL PROCESS EQUIPMENT COMPRISING APPLYING THERETO SPENT ALKYLATION SULFURIC ACID, DRAINING THE ACID FROM THE EQUIPMENT AFTER ABOUT 30 MINUTES AND FLUSHING THE EQUIPMENT WITH AQUEOUS SOLVENT. 